One of the biggest problems with TDD (and agile), in my opinion, is that it lacks an objective feedback mechanism that makes it obvious whether it's being applied correctly. I believe any methodology must have built-in feedback to ensure that it's applied correctly to be practical or successful. It takes a human TDD guru to subjectively determine if a team is doing TDD "right" or not. Whereas other development practices, such as producing daily builds, have obvious channels of direct feedback (do you produce a build every day, is it broken, does it use up-to-date sources, etc.). I believe that aspects of TDD will ultimately become part of a larger set of methodologies which together provide obvious, measurable benefits to development of many if not most software projects. But today the case for TDD as a one-size-fits-all methodology is far from conclusive.
